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ValidBST.cpp
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ValidBST.cpp
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#include <iostream>
#include <climits>
class TreeNode {
public:
TreeNode(int n):val(n), right(NULL), left(NULL) {}
int val;
TreeNode* right;
TreeNode* left;
};
bool isBSTHelper(TreeNode* root, int& prev) {
if (!root) return true;
if (!(isBSTHelper(root->left, prev))) {
std::cout << "1" << std::endl;
return false;
}
if (!((root->val> prev) && (prev = root->val))) {
std::cout << "2" << std::endl;
return false;
}
if (!isBSTHelper(root->right, prev)) {
std::cout << "3" << std::endl;
return false;
}
return true;
}
bool isBST(TreeNode *root) {
int prev = INT_MIN;
return isBSTHelper(root, prev);
}
int main() {
TreeNode* root =new TreeNode(0);
TreeNode* left = new TreeNode(-1);
TreeNode* right = new TreeNode(2);
// root->left = left;
// root->right = right;
if (isBST(root)) std::cout << "T" << std::endl;
else std::cout << "F" << std::endl;
return 0;
}